The present invention relates to an isolating device for a calibrated safety valve for positioning in a circuit upstream of a safety valve in order to isolate the latter should it remain accidentally locked in the open position.
Operating defects of safety valve on closing can have disastrous consequences, because they lead both to a pressure drop in the circuit which they are responsible for monitoring and to an uncontrolled escape of the fluid contained in the said circuit. This is in particular the case when such faults occur on certain valves equipping the primary cooling circuit of a nuclear power station. Thus, the failure to close of these valves can be looked upon as a breach of the primary circuit and this must be effectively remedied as rapidly as possible. Hitherto, no satisfactory solution of this problem is known.
Thus, although it is known to protect a discharge cock by placing a valve upstream thereof this solution cannot be used for protecting a safety valve for obvious safety reasons. Thus, merely isolating the defective valve would lead to the elimination of the protection of the overpressure circuit. Moreover, the same result would be obtained if the isolating valve was accidentally operated in normal operation.